U.S. patent number 6,254,626 [Application Number 09/215,041] was granted by the patent office on 2001-07-03 for articulation device for selective organ cooling apparatus.
This patent grant is currently assigned to Innercool Therapies, Inc.. Invention is credited to John D. Dobak, III, Juan C. Lasheras.
United States Patent |
6,254,626 |
Dobak, III , et al. |
July 3, 2001 |
Articulation device for selective organ cooling apparatus
Abstract
A selective organ heat transfer device with deep irregularities
in a turbulence-inducing exterior surface. The device can have a
plurality of elongated, articulated segments, each having a
turbulence-inducing exterior surface. A flexible joint connects
adjacent elongated, articulated segments. The flexible joint may be
a rubber tube or a metal tube of a predetermined thickness. An
inner lumen is disposed within the heat transfer segments. The
inner lumen is capable of transporting a pressurized working fluid
to a distal end of the heat transfer element.
Inventors: |
Dobak, III; John D. (La Jolla,
CA), Lasheras; Juan C. (La Jolla, CA) |
Assignee: |
Innercool Therapies, Inc. (San
Diego, CA)
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Family
ID: |
46256219 |
Appl.
No.: |
09/215,041 |
Filed: |
December 16, 1998 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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103342 |
Jun 23, 1998 |
6096068 |
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052545 |
Mar 31, 1998 |
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047012 |
Mar 24, 1998 |
5957963 |
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Current U.S.
Class: |
607/105; 607/104;
607/106 |
Current CPC
Class: |
A61B
18/02 (20130101); A61F 7/12 (20130101); A61M
25/00 (20130101); A61B 2017/00292 (20130101); A61B
2018/0022 (20130101); A61B 2018/0212 (20130101); A61F
2007/0056 (20130101); A61F 2007/126 (20130101); A61M
25/0023 (20130101); A61M 2025/0004 (20130101); A61M
2025/006 (20130101); A61M 2205/3606 (20130101) |
Current International
Class: |
A61M
25/00 (20060101); A61F 7/12 (20060101); A61F
7/00 (20060101); A61F 007/00 () |
Field of
Search: |
;607/104-106
;606/20,21,22,23 ;604/93,52,53 ;165/142,179,181,184 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0655225 A1 |
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May 1993 |
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EP |
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0 664 990 |
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Nov 1997 |
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EP |
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2 447 406 |
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Mar 1980 |
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FR |
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806 029 |
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Feb 1981 |
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SU |
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WO 91/05528 |
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May 1991 |
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WO |
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WO 93/04727 |
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Mar 1993 |
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WO |
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WO 95/01814 |
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Jan 1995 |
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WO |
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WO 96/40347 |
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Dec 1996 |
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WO |
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WO 97/01374 |
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Jan 1997 |
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WO |
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WO 97/25011 |
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Jul 1997 |
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WO |
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WO 98/26831 |
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Jun 1998 |
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WO |
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WO 98/31312 |
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Jul 1998 |
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WO |
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Other References
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Primary Examiner: Dvorak; Linda C. M.
Assistant Examiner: Kearney; R.
Attorney, Agent or Firm: Wieczorek; Mark D.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This is a continuation-in-part patent application of U.S. patent
applications Ser. No. 09/103,342, filed on Jun. 23, 1998, and
entitled "Selective Organ Cooling Catheter and Method of Using the
Same" U.S. Pat. No. 6,096,068 and U.S. Ser. No. 09/052,545, filed
on Mar. 31, 1998, and entitled "Circulating Fluid Hypothermria
Method and Apparatus" and U.S. Ser. No. 09/047,012, filed on Mar.
24, 1998, and entitled "Improved Selective Organ Hypothermia Method
and Apparatus" U.S. Pat. No. 5,957,963, the entirety of each being
incorporated by reference herein.
Claims
What is claimed is:
1. A selective brain cooling device, comprising:
a flexible catheter capable of insertion to a carotid artery of a
patient;
a heat transfer element attached to a distal end of said catheter,
said heat transfer element including a plurality of heat transfer
segments, further including a flexible metal tube connecting each
of said heat transfer segments to adjacent said heat transfer
segments, and wherein said flexible metal tube has a wall thickness
of between about 0.5 and 0.8 mils and a diameter of between about 2
and 4 mm;
a plurality of exterior helical ridges on said heat transfer
element, said helical ridges to create mixing in a blood flow in
the carotid artery; and
an inner coaxial tube disposed within said heat transfer element,
said inner coaxial tube being connected in fluid flow communication
with an inner coaxial tube within said catheter.
2. A selective brain cooling device, comprising:
a flexible catheter capable of insertion to a carotid artery of a
patient;
a heat transfer element attached to a distal end of said catheter,
said heat transfer element including a plurality of heat transfer
segments, further including a flexible rubber tube connecting each
of said heat transfer segments to adjacent said heat transfer
segments, and wherein said flexible rubber tube has a diameter of
between about 2 and 4 mm;
a plurality of exterior helical ridges on said heat transfer
element, said helical ridges to create mixing in a blood flow in
the carotid artery; and
an inner coaxial tube disposed within said heat transfer element,
said inner coaxial tube being connected in fluid flow communication
with an inner coaxial tube within said catheter.
Description
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
BACKGROUND OF THE INVETION
1. Field of the Invention
The present invention relates generally to the modification and
control of the temperature of a selected body organ. More
particularly, the invention relates to a method and intravascular
apparatus for controlling organ temperature.
2. Background Information
Organs in the human body, such as the brain, kidney and heart, are
maintained at a constant temperature of approximately 37.degree. C.
Hypothermia can be clinically defined as a core body temperature of
35.degree. C. or less. Hypothermia is sometimes characterized
further according to its severity. A body core temperature in the
range of 33.degree. C. to 35.degree. C. is described as mild
hypothermia. A body temperature of 28.degree. C. to 32.degree. C.
is described as moderate hypothermia. A body core temperature in
the range of 24.degree. C. to 28.degree. C. is described as severe
hypothermia.
Hypothermia is uniquely effective in reducing brain injury caused
by a variety of neurological insults and may eventually play an
important role in emergency brain resuscitation. Experimental
evidence has demonstrated that cerebral cooling improves outcome
after global ischemia, focal ischemia, or traumatic brain injury.
For this reason, hypothermia may be induced in order to reduce the
effect of certain bodily injuries to the brain as well as other
organs.
Cerebral hypothermia has traditionally been accomplished through
whole body cooling to create a condition of total body hypothermia
in the range of 20.degree. C. to 30.degree. C. However, the use of
total body hypothermia risks certain deleterious systematic
vascular effects. For example, total body hypothermia may cause
severe derangement of the cardiovascular system, including low
cardiac output, elevated systematic resistance, and ventricular
fibrillation. Other side effects include renal failure,
disseminated intravascular coagulation, and electrolyte
disturbances. In addition to the undesirable side effects, total
body hypothermia is difficult to administer.
Catheters have been developed which are inserted into the
bloodstream of the patient in order to induce total body
hypothermia. For example, U.S. Pat. No. 3,425,419 to Dato describes
a method and apparatus of lowering and raising the temperature of
the human body. Dato induces moderate hypothermia in a patient
using a metallic catheter. The metallic catheter has an inner
passageway through which a fluid, such as water, can be circulated.
The catheter is inserted through the femoral vein and then through
the inferior vena cava as far as the right atrium and the superior
vena cava. The Dato catheter has an elongated cylindrical shape and
is constructed from stainless steel. By way of example, Dato
suggests the use of a catheter approximately 70 cm in length and
approximately 6 mm in diameter. However, use of the Dato device
implicates the negative effects of total body hypothemiia described
above.
Due to the problems associated with total body hypothermia,
attempts have been made to provide more selective cooling. For
example, cooling helmets or head gear have been used in an attempt
to cool only the head rather than the patient's entire body.
However, such methods rely on conductive heat transfer through the
skull and into the brain. One drawback of using conductive heat
transfer is that the process of reducing the temperature of the
brain is prolonged. Also, it is difficult to precisely control the
temperature of the brain when using conduction due to the
temperature gradient that must be established externally in order
to sufficiently lower the internal temperature. In addition, when
using conduction to cool the brain, the face of the patient is also
subjected to severe hypothermia, increasing discomfort and the
likelihood of negative side effects. It is known that profound
cooling of the face can cause similar cardiovascular side effects
as total body cooling. From a practical standpoint, such devices
are cumbersome and may make continued treatment of the patient
difficult or impossible.
Selected organ hypothermia has been accomplished using
extracorporeal perfusion, as detailed by Arthur E. Schwartz, M. D.
et al., in Isolated Cerebral Hypothermia by Single Carotid Artery
Perfusion of Extracorporeally Cooled Blood in Baboons, which
appeared in Vol. 39, No. 3, NEUROSURGERY 577 (September, 1996). In
this study, blood was continually withdrawn from baboons through
the femoral artery. The blood was cooled by a water bath and then
infused through a common carotid artery with its external branches
occluded. Using this method, normal heart rhyttin, systemic
arterial blood pressure and arterial blood gas values were
maintained during the hypothermia. This study showed that the brain
could be selectively cooled to temperatures of 20.degree. C.
without reducing the temperature of the entire body. However,
external circulation of blood is not a practical approach for
treating humans because the risk of infection, need for
anticoagulation, and risk of bleeding is too great. Further, this
method requires cannulation of two vessels making it more
cumbersome to perform particularly in emergency settings. Even
more, percutaneous cannulation of the carotid artery is difficult
and potentially fatal due to the associated arterial wall trauma.
Finally, this method would be ineffective to cool other organs,
such as the kidneys, because the feeding arteries cannot be
directly cannulated percutaneously.
Selective organ hypothermia has also been attempted by perfusion of
a cold solution such as saline or perflourocarbons. This process is
commonly used to protect the heart during heart surgery and is
referred to as cardioplegia. Perfusion of a cold solution has a
number of drawbacks, including a limited time of administration due
to excessive volume accumulation, cost, and inconvenience of
maintaining the perfusate and lack of effectiveness due to the
temperature dilution from the blood. Temperature dilution by the
blood is a particular problem in high blood flow organs such as the
brain.
Therefore, a practical method and apparatus which modifies and
controls the temperature of a selected organ satisfies a long-felt
need.
BRIEF SUMMARY OF THE INVENTION
The apparatus of the present invention can, by way of example only,
include a heat transfer element which comprises first and second
elongated, articulated segments, each segment having a
turbulence-inducing exterior surface. A flexible joint can connect
the first and second elongated segments. An inner coaxial lumen may
be disposed within the first and second elongated segments and is
capable of transporting a pressurized working fluid to a distal end
of the first elongated segment. In addition, the first and second
elongated segments may have a turbulence-inducing interior surface
for inducing turbulence within the pressurized working fluid. The
turbulence-inducing exterior surface may be adapted to induce
turbulence within a free stream of blood flow when placed within an
artery. The turbulence-inducing exterior surface may be adapted to
induce a turbulence intensity greater than 0.05 within a free
stream blood flow. In one embodiment, the flexible joint comprises
a straight tube having a predetermined thickness which allows for
lateral bending of the heat transfer element.
In one embodiment, the turbulence-inducing exterior surfaces of the
heat transfer element comprise one or more helical ridges
configured to have a depth which is greater than a thickness of a
boundary layer of blood which develops within an arterial blood
flow. Adjacent segments of the heat transfer element can be
oppositely spiraled to increase turbulence. For instance, the first
elongated heat transfer segment may comprise one or more helical
ridges having a counter-clockwise twist, while the second elongated
heat transfer segment comprises one or more helical ridges having a
clockwise twist. Alternatively, of course, the first elongated heat
transfer segment may comprise one or more clockwise helical ridges,
and the second elongated heat transfer segment may comprise one or
more counter-clockwise helical ridges. The first and second
elongated, articulated segments may be formed from highly
conductive materials.
In another embodiment, the turbulence-inducing exterior surface of
the heat transfer element is adapted to induce turbulence
throughout the duration of each pulse of a pulsatile blood flow
when placed within an artery. In still another embodiment, the
turbulence-inducing exterior surface of the heat transfer element
is adapted to induce turbulence during at least 20% of the period
of each cardiac cycle when placed within an artery.
The heat transfer device may also have a coaxial supply catheter
with an inner catheter lumen coupled to the inner coaxial lumen
within the first and second elongated heat transfer segments. A
working fluid supply configured to dispense the pressurized working
fluid may be coupled to the inner catheter lumen. The working fluid
supply may be configured to produce the pressurized working fluid
at a temperature of about 0.degree. C. and at a pressure below
about 5 atmospheres of pressure.
In yet another alternative embodiment, the heat transfer device may
have three or more elongated, articulated, heat transfer segments
having a turbulence-inducing exterior surface, with additional
flexible joints connecting the additional elongated heat transfer
segments. In one such embodiment, by way of example, the first and
third elongated heat transfer segments may comprise clockwise
helical ridges, and the second elongated heat transfer segment may
comprise one or more counter-clockwise helical ridges.
Alternatively, of course, the first and third elongated heat
transfer segments may comprise counter-clockwise helical ridges,
and the second elongated heat transfer segment may comprise one or
more clockwise helical ridges.
The turbulence-inducing exterior surface of the heat transfer
element may optionally include a surface coating or treatment to
inhibit clot formation. One variation of the heat transfer element
comprises a stent coupled to a distal end of the first elongated
heat transfer segment.
In one embodiment, the catheter has a flexible metal tip and the
cooling step occurs at the tip. The tip may have
turbulence-inducing elongated heat transfer segments separated by
metal pipe sections or flexible polymer sections. The
turbulence-inducing segments may comprise helical ridges which are
configured to have a depth which is greater than a thickness of a
boundary layer of blood which develops within the blood vessel. In
another embodiment, the catheter has a tip at which the cooling
step occurs and the tip has turbulence-inducing elongated heat
transfer segments that alternately spiral bias the surrounding
blood flow in clockwise and counterclockwise directions.
The present invention also envisions a cooling catheter comprising
a catheter shaft having first and second lumens therein. The
cooling catheter also comprises a cooling tip adapted to transfer
heat to or from a working fluid circulated in through the first
lumen and out through the second lumen, and turbulence-inducing
structures on the cooling tip capable of inducing free stream
turbulence when the tip is inserted into a blood vessel. The
turbulence-inducing structures may induce a turbulence intensity of
at least about 0.05. The cooling tip may be adapted to induce
turbulence within the working fluid. The catheter is capable of
removing at least about 25 Watts of heat from an organ when
inserted into a vessel supplying that organ, while cooling the tip
with a working fluid that remains a liquid in the catheter.
Alternatively, the catheter is capable of removing at least about
50 or 75 Watts of heat from an organ when inserted into a vessel
supplying that organ, while cooling the tip with an aqueous working
fluid. In one embodiment, in use, the tip has a diameter of about 4
mm or less. Optionally, the turbulence-inducing surfaces on the
heat transfer segments comprise helical ridges which have a depth
sufficient to disrupt the free stream blood flow in the blood
vessel. Alternatively, the turbulence-inducing surfaces may
comprise staggered protrusions from the outer surfaces of the heat
transfer segments, which have a height sufficient to disrupt the
free stream flow of blood within the blood vessel.
In another embodiment, a cooling catheter may comprise a catheter
shaft having first and second lumens therein, a cooling tip adapted
to transfer heat to or from a working fluid circulated in through
the first lumen and out through the second lumen, and
turbulence-inducing structures on the cooling tip capable of
inducing turbulence when the tip is inserted into a blood vessel.
Alternatively, a cooling catheter may comprise a catheter shaft
having first and second lumens therein, a cooling tip adapted to
transfer heat to or from a working fluid circulated in through the
first lumen and out through the second lumen, and structures on the
cooling tip capable of inducing free stream turbulence when the tip
is inserted into a blood vessel. In another embodiment, a cooling
catheter may comprise a catheter shaft having first and second
lumens therein, a cooling tip adapted to transfer heat to or from a
working fluid circulated in through the first lumen and out through
the second lumen, and turbulence-inducing structures on the cooling
tip capable of inducing turbulence with an intensity greater than
about 0.05 when the tip is inserted into a blood vessel.
The novel features of this invention, as well as the invention
itself, will be best understood from the attached drawings, taken
along with the following description, in which similar reference
characters refer to similar parts, and in which:
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
FIG. 1 is an elevation view of a turbulence inducing heat transfer
element within an artery;
FIG. 2 is an elevation view of one embodiment of a heat transfer
element which may be employed according to the invention;
FIG. 3 is longitudinal section view of the heat transfer element of
FIG. 2;
FIG. 4 is a transverse section view of the heat transfer element of
FIG. 2;
FIG. 5 is a persp ective view of the heat transfer element of FIG.
2 in use within a blood vessel;
FIG. 6 is a cut-away perspective view of an alternative embodiment
of a heat transfer element which may be employed according to the
invention;
FIG. 7 is a transverse section view of the heat transfer element of
FIG. 6; and
FIG. 8 is a schematic representation of the invention being used in
one embodiment to cool the brain of a patient.
DETAILED DESCRIPTION OF THE TNVENTION
The temperature of a selected organ may be intravascularly
regulated by a heat transfer element placed in the organ's feeding
artery to absorb or deliver heat to or from the blood flowing into
the organ. While the method is described with respect to blood flow
into an organ, it is understood that heat transfer within a volume
of tissue is analogous. In the latter case, heat transfer is
predominantly by conduction.
The heat transfer may cause either a cooling or a heating of the
selected organ. A heat transfer element that selectively alters the
temperature of an organ should be capable of providing the
necessary heat transfer rate to produce the desired cooling or
heating effect within the organ to achieve a desired
temperature.
The heat transfer element should be small and flexible enough to
fit within the feeding artery while still allowing a sufficient
blood flow to reach the organ in order to avoid ischeniic organ
damage. Feeding arteries, like the carotid artery, branch off the
aorta at various levels. Subsidiary arteries continue to branch off
these initial branches. For example, the internal carotid artery
branches off the common carotid artery near the angle of the jaw.
The heat transfer element is typically inserted into a peripheral
artery, such as the femoral artery, using a guide catheter or guide
wire, and accesses a feeding artery by initially passing though a
series of one or more of these branches. Thus, the flexibility and
size, e.g., the diameter, of the heat transfer element are
important characteristics. This flexibility is achieved as is
described in more detail below.
These points are illustrated using brain cooling as an example. The
common carotid artery supplies blood to the head and brain. The
internal carotid artery branches off the common carotid artery to
supply blood to the anterior cerebrum. The heat transfer element
may be placed into the common carotid artery or into both the
common carotid artery and the internal carotid artery.
The benefits of hypothermia described above are achieved when the
temperature of the blood flowing to the brain is reduced to between
30.degree. C. and 32.degree. C. A typical brain has a blood flow
rate through each carotid artery (right and left) of approximately
250-375 cubic centimeters per minute (cc/min). With this flow rate,
calculations show that the heat transfer element should absorb
approximately 75-175 watts of heat when placed in one of the
carotid arteries to induce the desired cooling effect. Smaller
organs may have less blood flow in their respective supply arteries
and may require less heat transfer, such as about 25 watts.
The method employs conductive and convective heat transfers. Once
the materials for the device and a working fluid are chosen, the
conductive heat transfers are solely dependent on the temperature
gradients. Convective heat transfers, by contrast, also rely on the
movement of fluid to transfer heat. Forced convection results when
the heat transfer surface is in contact with a fluid whose motion
is induced (or forced) by a pressure gradient, area variation, or
other such force. In the case of arterial flow, the heating heart
provides an oscillatory pressure gradient to force the motion of
the blood in contact with the heat transfer surface. One of the
aspects of the device uses turbulence to enhance this forced
convective heat transfer.
The rate of convective heat transfer Q is proportional to the
product of S, the area of the heat transfer element in direct
contact with the fluid, .DELTA.T=T.sub.b -T.sub.s, the temperature
differential between the surface temperature T.sub.s of the heat
transfer element and the free stream blood temperature T.sub.b, and
h.sub.c +L , the average convection heat transfer coefficient over
the heat transfer area. h.sub.c +L is sometimes called the "surface
coefficient of heat transfer" or the "convection heat transfer
coefficient".
The magnitude of the heat transfer rate Q to or from the fluid flow
can be increased through manipulation of the above three
parameters. Practical constraints limit the value of these
parameters and how much they can be manipulated. For example, the
internal diameter of the common carotid artery ranges from 6 to 8
mm. Thus, the heat transfer element residing therein may not be
much larger than 4 mm in diameter to avoid occluding the vessel.
The length of the heat transfer element should also be limited. For
placement within the internal and common carotid artery, the length
of the heat transfer element is limited to about 10 cm. This
estimate is based on the length of the common carotid artery, which
ranges from 8 to 12 cm.
Consequently, the value of the surface area S is limited by the
physical constraints imposed by the size of the artery into which
the device is placed. Surface features, such as fins, can be used
to increase the surface area of the heat transfer element, however,
these features alone cannot provide enough surface area enhancement
to meet the required heat transfer rate to effectively cool the
brain.
One may also attempt to vary the magnitude of the heat transfer
rate by varying .DELTA.T. The value of .DELTA.T=T.sub.b -T.sub.s
can be varied by varying the surface temperature T.sub.s of the
heat transfer element. The allowable surface temperature of the
heat transfer element is limited by the characteristics of blood.
The blood temperature is fixed at about 37.degree. C., and blood
freezes at approximately 0.degree. C. When the blood approaches
freezing, ice emboli may form in the blood which may lodge
downstream, causing serious ischemic injury. Furthermore, reducing
the temperature of the blood also increases its viscosity which
results in a small decrease in the value of h.sub.c +L . Increased
viscosity of the blood may further result in an increase in the
pressure drop within the artery, thus compromising the flow of
blood to the brain. Given the above constraints, it is advantageous
to limit the surface temperature of the heat transfer element to
approximately 1.degree. C.-5.degree. C., thus resulting in a
maximum temperature differential between the blood stream and the
heat transfer element of approximately 32.degree. C.-36.degree.
C.
One may also attempt to vary the magnitude of the heat transfer
rate by varying h.sub.c +L . Fewer constraints are imposed on the
value of the convection heat transfer coefficient h.sub.c +L . The
mechanisms by which the value of .sub.c +L may be increased are
complex. However, one way to increase h.sub.c +L for a fixed mean
value of the velocity is to increase the level of turbulent kinetic
energy in the fluid flow.
The heat transfer rate Q.sub.no-flow in the absence of fluid flow
is proportional to .DELTA.T, the temperature differential between
the surface temperature T.sub.s of the heat transfer element and
the free stream blood temperature T.sub.b times k, the diffusion
constant, and is inversely proportion to .delta., the thickness of
the boundary layer.
The magnitude of the enhancement in heat transfer by fluid flow can
be estimated by taking the ratio of the heat transfer rate with
fluid flow to the heat transfer rate in the absence of fluid flow
N=Q.sub.flow /Q.sub.no-flow =h.sub.c +L /(k/.delta.). This ratio is
called the Nusselt number ("Nu"). For convective heat transfer
between blood and the surface of the heat transfer element, Nusselt
numbers of 30-80 have been found to be appropriate for selective
cooling applications of various organs in the human body. Nusselt
numbers are generally dependent on several other numbers: the
Reynolds number, the Womersley number, and the Prandt1 number.
Stirring-type mechanisms, which abruptly change the direction of
velocity vectors, may be utilized to induce turbulent kinetic
energy and increase the heat transfer rate. The level of turbulence
so created is characterized by the turbulence intensity .theta..
Turbulence intensity .theta. is defined as the root mean square of
the fluctuating velocity divided by the mean velocity. Such
mechanisms can create high levels of turbulence intensity in the
free stream, thereby increasing the heat transfer rate. This
turbulence intensity should ideally be sustained for a significant
portion of the cardiac cycle, and should ideally be created
throughout the free stream and not just in the boundary layer.
Turbulence does occur for a short period in the cardiac cycle
anyway. In particular, the blood flow is turbulent during a small
portion of the descending systolic flow. This portion is less than
20% of the period of the cardiac cycle. If a heat transfer element
is placed co-axially inside the artery, the heat transfer rate will
be enhanced during this short interval. For typical of these
fluctuations, the turbulence intensity is at least 0.05. In other
words, the instantaneous velocity fluctuations deviate from the
mean velocity by at least 5%. Although ideally turbulence is
created throughout the entire period of the cardiac cycle, the
benefits of turbulence are obtained if the turbulence is sustained
for 75%, 50% or even as low as 30% or 20% of the cardiac cycle.
One type of turbulence-inducing heat transfer element which may be
advantageously employed to provide heating or cooling of an organ
or volume is described in co-pending U.S. patent application Ser.
No. 09/103,342 to Dobak and Lasheras for a "Selective Organ Cooling
Catheter and Method of Using the Same," incorporated by reference
above. In that application, and as described below, the heat
transfer element is made of a high thermal conductivity material,
such as metal. The use of a highly thermally conductive material
increases the heat transfer rate for a given temperature
differential between the coolant within the heat transfer element
and the blood. This facilitates the use of a higher temperature
coolant within the heat transfer element, allowing safer coolants,
such as water, to be used. Highly thermally conductive materials,
such as metals, tend to be rigid. In that application, bellows
provided a high degree of articulation that compensated for the
intrinsic stiffness of the metal. In the present application, the
bellows are replaced with a straight metal tube having a
predetermined thickness to allow flexibility via bending of the
metal. Alternatively, the bellows may be replaced with a polymer
tube, e.g., a latex rubber tube, a plastic tube, a corrugated
plastic tube, etc.
The device size may be minimized, e.g., less than 4 mm, to prevent
blockage of the blood flowing in the artery. The design of the heat
transfer element should facilitate flexibility in an inherently
inflexible material.
To create the desired level of turbulence intensity in the blood
free stream during the whole cardiac cycle, one embodiment of the
device uses a modular design. This design creates helical blood
flow and produces a high level of turbulence in the free stream by
periodically forcing abrupt changes in the direction of the helical
blood flow. FIG. 1 is a perspective view of such a turbulence
inducing heat transfer element within an artery. Turbulent flow
would be found at point 114, in the free stream area The abrupt
changes in flow direction are achieved through the use of a series
of two or more heat transfer segments, each comprised of one or
more helical ridges. To affect the free stream, the depth of the
helical ridge is larger than the thickness of the boundary layer
which would develop if the heat transfer element had a smooth
cylindrical surface.
The use of periodic abrupt changes in the helical direction of the
blood flow in order to induce strong free stream turbulence may be
illustrated with reference to a common clothes washing machine. The
rotor of a washing machine spins initially in one direction causing
laminar flow. When the rotor abruptly reverses direction,
significant turbulent kinetic energy is created within the entire
wash basin as the changing currents cause random turbulent motion
within the clothes-water slurry.
FIG. 2 is an elevation view of one embodiment of a heat transfer
element 14. The heat transfer element 14 is comprised of a series
of elongated, articulated segments or modules 20, 22, 24. Three
such segments are shown in this embodiment, but two or more such
segments could be used. As seen in FIG. 2, a first elongated heat
transfer segment 20 is located at the proximal end of the heat
transfer element 14. A turbulence-inducing exterior surface of the
segment 20 comprises four parallel helical ridges 28 with four
parallel helical grooves 26 therebetween. One, two, three, or more
parallel helical ridges 28 could also be used. In this embodiment,
the helical ridges 28 and the helical grooves 26 of the heat
transfer segment 20 have a left hand twist, referred to herein as a
counter-clockwise spiral or helical rotation, as they proceed
toward the distal end of the heat transfer segment 20.
The first heat transfer segment 20 is coupled to a second elongated
heat transfer segment 22 by a first tube section 25, which provides
flexibility. The second heat transfer segment 22 comprises one or
more helical ridges 32 with one or more helical grooves 30
therebetween. The ridges 32 and grooves 30 have a right hand, or
clockwise, twist as they proceed toward the distal end of the heat
transfer segment 22. The second heat transfer segment 22 is coupled
to a third elongated heat transfer segment 24 by a second tube
section 27. The third heat transfer segment 24 comprises one or
more helical ridges 36 with one or more helical grooves 34
therebetween. The helical ridge 36 and the helical groove 34 have a
left hand, or counter-clockwise, twist as they proceed toward the
distal end of the heat transfer segment 24. Thus, successive heat
transfer segments 20, 22, 24 of the heat transfer element 14
alternate between having clockwise and counterclockwise helical
twists. The actual left or right hand twist of any particular
segment is immaterial, as long as adjacent segments have opposite
helical twist.
In addition, the rounded contours of the ridges 28, 32, 36 also
allow the heat transfer element 14 to maintain a relatively
atraumatic profile, thereby minimizing the possibility of damage to
the blood vessel wall. A heat transfer element may be comprised of
two, three, or more heat transfer segments.
The tube sections 25, 27 are formed from seamless and nonporous
materials, such as metal, and therefore are impermeable to gas,
which can be particularly important, depending on the type of
working fluid which is cycled through the heat transfer element 14.
The structure of the tube sections 25, 27 allows them to bend,
extend and compress, which increases the flexibility of the heat
transfer element 14 so that it is more readily able to navigate
through blood vessels. The tube sections 25, 27 are also able to
tolerate cryogenic temperatures without a loss of performance. The
tube sections 25, 27 may have a predetermined thickness of their
walls, such as between about 0.5 and 0.8 mils. The predetermined
thickness is to a certain extent dependent on the diameter of the
overall tube. Thicknesses of 0.5 to 0.8 mils may be appropriate
especially for a tubal diameter of about 4 mm. For smaller
diameters, such as about 3.3 mm, larger thicknesses may be employed
for higher strength. In another embodiment, tube sections 25, 27
may be formed from a polymer material such as rubber, e.g. latex
rubber, plastic, corrugated plastic, etc.
The exterior surfaces of the heat transfer element 14 can be made
from metal except in flexible joint embodiment where the surface
may be comprised of a polymer material. The metal may be a very
high thermal conductivity material such as nickel, thereby
facilitating efficient heat transfer. Alternatively, other metals
such as stainless steel, titanium, aluminum, silver, copper and the
like, can be used, with or without an appropriate coating or
treatment to enhance biocompatibility or inhibit clot formation.
Suitable biocompatible coatings include, e.g., gold, platinum or
polymer paralyene. The heat transfer element 14 may be manufactured
by plating a thin layer of metal on a mandrel that has the
appropriate pattern. In this way, the heat transfer element 14 may
be manufactured inexpensively in large quantities, which is an
important feature in a disposable medical device.
Because the heat transfer element 14 may dwell within the blood
vessel for extended periods of time, such as 24-48 hours or even
longer, it may be desirable to treat the surfaces of the heat
transfer element 14 to avoid clot formation. One means by which to
prevent thrombus formation is to bind an antithrombogenic agent to
the surface of the heat transfer element 14. For example, heparin
is known to inhibit clot formation and is also known to be useful
as a biocoating. Alternatively, the surfaces of the heat transfer
element 14 may be bombarded with ions such as nitrogen. Bombardment
with nitrogen can harden and smooth the surface and, thus prevent
adherence of clotting factors to the surface.
FIG. 3 is a longitudinal sectional view of the heat transfer
element 14, taken along line 3--3 in FIG. 2. Some interior contours
are omitted for purposes of clarity. An inner tube 42 creates an
inner coaxial lumen 42 and an outer coaxial lumen 46 within the
heat transfer element 14. Once the heat transfer element 14 is in
place in the blood vessel, a working fluid such as saline or other
aqueous solution may be circulated through the heat transfer
element 14. Fluid flows up a supply catheter into the inner coaxial
lumen 40. At the distal end of the heat transfer element 14, the
working fluid exits the inner coaxial lumen 40 and enters the outer
lumen 46. As the working fluid flows through the outer lumen 46,
heat is transferred from the working fluid to the exterior surface
37 of the heat transfer element 14. Because the heat transfer
element 14 is constructed from a high conductivity material, the
temperature of its exterior surface 37 may reach very close to the
temperature of the working fluid. The tube 42 may be formed as an
insulating divider to thermally separate the inner lumen 40 from
the outer lumen 46. For example, insulation may be achieved by
creating longitudinal air channels in the wall of the insulating
tube 42. Alternatively, the insulating tube 42 may be constructed
of a non-thermally conductive material like polytetrafluoroethylene
or some other polymer.
It is important to note that the same mechanisms that govern the
heat transfer rate between the exterior surface 37 of the heat
transfer element 14 and the blood also govern the heat transfer
rate between the working fluid and the interior surface 38 of the
heat transfer element 14. The heat transfer characteristics of the
interior surface 38 are particularly important when using water,
saline or other fluid which remains a liquid as the coolant. Other
coolants such as freon undergo nucleate boiling and create
turbulence through a different mechanism. Saline is a safe coolant
because it is non-toxic, and leakage of saline does not result in a
gas embolism, which could occur with the use of boiling
refrigerants. Since turbulence in the coolant is enhanced by the
shape of the interior surface 38 of the heat transfer element 14,
the coolant can be delivered to the heat transfer element 14 at a
warmer temperature and still achieve the necessary heat transfer
rate.
This has a number of beneficial implications in the need for
insulation along the catheter shaft length. Due to the decreased
need for insulation, the catheter shaft diameter can be made
smaller. The enhanced heat transfer characteristics of the interior
surface of the heat transfer element 14 also allow the working
fluid to be delivered to the heat transfer element 14 at lower flow
rates and lower pressures. High pressures may make the heat
transfer element stiff and cause it to push against the wall of the
blood vessel, thereby shielding part of the exterior surface 37 of
the heat transfer element 14 from the blood. Because of the
increased heat transfer characteristics achieved by the alternating
helical ridges 28, 32, 36, the pressure of the working fluid may be
as low as 5 atmospheres, 3 atmospheres, 2 atmospheres or even less
than 1 atmosphere.
FIG. 4 is a transverse sectional view of the heat transfer element
14, taken at a location denoted by the line 4--4 in FIG. 2. FIG. 4
illustrates a five-lobed embodiment, whereas FIG. 2 illustrates a
four-lobed embodiment. As mentioned earlier, any number of lobes
might be used. In FIG. 4, the coaxial construction of the heat
transfer element 14 is clearly shown. The inner coaxial lumen 40 is
defined by the insulating coaxial tube 42. The outer lumen 46 is
defined by the exterior surface of the insulating coaxial tube 42
and the interior surface 38 of the heat transfer element 14. In
addition, the helical ridges 32 and helical grooves 30 may be seen
in FIG. 4. As noted above, in the preferred embodiment, the depth
of the grooves, d.sub.i, is greater than the boundary layer
thickness which would have developed if a cylindrical heat transfer
element were introduced. For example, in a heat transfer element 14
with a 4 mm outer diameter, the depth of the invaginations,
d.sub.i, may be approximately equal to 1 mm if designed for use in
the carotid artery. Although FIG. 4 shows four ridges and four
grooves, the number of ridges and grooves may vary. Thus, heat
transfer elements with 1, 2, 3, 4, 5, 6, 7, 8 or more ridges are
specifically contemplated.
FIG. 5 is a perspective view of a heat transfer element 14 in use
within a blood vessel, showing only one helical lobe per segment
for purposes of clarity. Beginning from the proximal end of the
heat transfer element (not shown in FIG. 5), as the blood moves
forward during the systolic pulse, the first helical heat transfer
segment 20 induces a counter-clockwise rotational inertia to the
blood. As the blood reaches the second segment 22, the rotational
direction of the inertia is reversed, causing turbulence within the
blood. Further, as the blood reaches the third segment 24, the
rotational direction of the inertia is again reversed. The sudden
changes in flow direction actively reorient and randomize the
velocity vectors, thus ensuring turbulence throughout the
bloodstream. During turbulent flow, the velocity vectors of the
blood become more random and, in some cases, become perpendicular
to the axis of the artery. In addition, as the velocity of the
blood within the artery decreases and reverses direction during the
cardiac cycle, additional turbulence is induced and turbulent
motion is sustained throughout the duration of each pulse through
the same mechanisms described above.
Thus, a large portion of the volume of warm blood in the vessel is
actively brought in contact with the heat transfer element 14,
where it can be cooled by direct contact rather than being cooled
largely by conduction through adjacent laminar layers of blood. As
noted above, the depth of the grooves 26, 30, 34 (FIG. 2) is
greater than the depth of the boundary layer which would develop if
a straight-walled heat transfer element were introduced into the
blood stream. In this way, free stream turbulence is induced. In
the preferred embodiment, in order to create the desired level of
turbulence in the entire blood stream during the whole cardiac
cycle, the heat transfer element 14 creates a turbulence intensity
greater than about 0.05. The turbulence intensity may be greater
than 0.05, 0.06, 0.07 or up to 0.10 or 0.20 or greater.
Referring back to FIG. 2, the heat transfer element 14 has been
designed to address all of the design criteria discussed above.
First, the heat transfer element 14 is flexible and is made of a
highly conductive material. The flexibility is provided by a
segmental distribution of tube sections 25, 27 which provide an
articulating mechanism. The tube sections have a predetermined
thickness which provides sufficient flexibility. Second, the
exterior surface area 37 has been increased through the use of
helical ridges 28, 32, 36 and helical grooves 26, 30, 34. The
ridges also allow the heat transfer element 14 to maintain a
relatively atraumatic profile, thereby minimizing the possibility
of damage to the vessel wall. Third, the heat transfer element 14
has been designed to promote turbulent kinetic energy both
internally and externally. The modular or segmental design allows
the direction of the invaginations to be reversed between segments.
The alternating helical rotations create an alternating flow that
results in mixing the blood in a manner analogous to the mixing
action created by the rotor of a washing machine that switches
directions back and forth. This mixing action is intended to
promote high level turbulent kinetic energy to enhance the heat
transfer rate. The alternating helical design also causes
beneficial mixing, or turbulent kinetic energy, of the working
fluid flowing internally.
FIG. 6 is a cut-away perspective view of an alternative embodiment
of a heat transfer element 50. An external surface 52 of the heat
transfer element 50 is covered with a series of axially staggered
protrusions 54. The staggered nature of the outer protrusions 54 is
readily seen with reference to FIG. 7 which is a transverse
cross-sectional sectional view taken at a location denoted by the
line 7--7 in FIG. 6. In order to induce free stream turbulence, the
height, d.sub.p, of the staggered outer protrusions 54 is greater
than the thickness of the boundary layer which would develop if a
smooth heat transfer element had been introduced into the blood
stream. As the blood flows along the external surface 52, it
collides with one of the staggered protrusions 54 and a turbulent
wake flow is created behind the protrusion. As the blood divides
and swirls along side of the first staggered protrusion 54, its
turbulent wake encounters another staggered protrusion 54 within
its path preventing the re-lamination of the flow and creating yet
more turbulence. In this way, the velocity vectors are randomized
and turbulence is created not only in the boundary layer but
throughout the free stream. As is the case with the preferred
embodiment, this geometry also induces a turbulent effect on the
internal coolant flow.
A working fluid is circulated up through an inner coaxial lumen 56
defined by an insulating coaxial tube 58 to a distal tip of the
heat transfer element 50. The working fluid then traverses an outer
coaxial lumen 60 in order to transfer heat to the exterior surface
52 of the heat transfer element 50. The inside surface of the heat
transfer element 50 is similar to the exterior surface 52, in order
to induce turbulent flow of the working fluid. The inner
protrusions can be aligned with the outer protrusions 54, as shown
in FIG. 7, or they can be offset from the outer protrusions 54, as
shown in FIG. 6.
FIG. 8 is a schematic representation of the invention being used to
cool the brain of a patient. The selective organ hypothermia
apparatus shown in FIG. 8 includes a working fluid supply 10,
preferably supplying a chilled liquid such as water, alcohol or a
halogenated hydrocarbon, a supply catheter 12 and the heat transfer
element 14. The supply catheter 12 has a coaxial construction. An
inner coaxial lumen within the supply catheter 12 receives coolant
from the working fluid supply 10. The coolant travels the length of
the supply catheter 12 to the heat transfer element 14 which serves
as the cooling tip of the catheter. At the distal end of the heat
transfer element 14, the coolant exits the insulated interior lumen
and traverses the length of the heat transfer element 14 in order
to decrease the temperature of the heat transfer element 14. The
coolant then traverses an outer lumen of the supply catheter 12 so
that it may be disposed of or recirculated. The supply catheter 12
is a flexible catheter having a diameter sufficiently small to
allow its distal end to be inserted percutaneously into an
accessible artery such as the femoral artery of a patient as shown
in FIG. 8. The supply catheter 12 is sufficiently long to allow the
heat transfer element 14 at the distal end of the supply catheter
12 to be passed through the vascular system of the patient and
placed in the internal carotid artery or other small artery. The
method of inserting the catheter into the patient and routing the
heat transfer element 14 into a selected artery is well known in
the art.
Although the working fluid supply 10 is shown as an exemplary
cooling device, other devices and working fluids may be used. For
example, in order to provide cooling, freon, perflourocarbon,
water, or saline may be used, as well as other such coolants.
The heat transfer element can absorb or provide over 75 Watts of
heat to the blood stream and may absorb or provide as much as 100
Watts, 150 Watts, 170 Watts or more. For example, a heat transfer
element with a diameter of 4 mm and a length of approximately 10 cm
using ordinary saline solution chilled so that the surface
temperature of the heat transfer element is approximately 5.degree.
C. and pressurized at 2 atmospheres can absorb about 100 Watts of
energy from the bloodstream. Smaller geometry heat transfer
elements may be developed for use with smaller organs which provide
60 Watts, 50 Watts, 25 Watts or less of heat transfer.
The practice of the present invention is illustrated in the
following non-limiting example.
Exemplary Procedure
1. The patient is initially assessed, resuscitated, and
stabilized.
2. The procedure is carried out in an angiography suite or surgical
suite equipped with flouroscopy.
3. Because the catheter is placed into the common carotid artery,
it is important to determine the presence of stenotic atheromatous
lesions. A carotid duplex (doppler/ultrasound) scan can quickly and
non-invasively make this determination. The ideal location for
placement of the catheter is in the left carotid so this may be
scanned first. If disease is present, then the right carotid artery
can be assessed. This test can be used to detect the presence of
proximal common carotid lesions by observing the slope of the
systolic upstroke and the shape of the pulsation. Although these
lesions are rare, they could inhibit the placement of the catheter.
Examination of the peak blood flow velocities in the internal
carotid can determine the presence of internal carotid artery
lesions. Although the catheter is placed proximally to such
lesions, the catheter may exacerbate the compromised blood flow
created by these lesions. Peak systolic velocities greater that 130
cm/sec and peak diastolic velocities greater than 100 cm/sec in the
internal indicate the presence of at least 70% stenosis. Stenosis
of 70% or more may warrant the placement of a stent to open up the
internal artery diameter.
4. The ultrasound can also be used to determine the vessel diameter
and the blood flow and the catheter with the appropriately sized
heat transfer element could be selected.
5. After assessment of the arteries, the patients inguinal region
is sterilely prepped and infiltrated with lidocaine.
6. The femoral artery is cannulated and a guide wire may be
inserted to the desired carotid artery. Placement of the guide wire
is confirmed with flouroscopy.
7. An angiographic catheter can be fed over the wire and contrast
media injected into the artery to further to assess the anatomy of
the carotid.
8. Alternatively, the femoral artery is cannulated and a 10-12.5
french (f) introducer sheath is placed.
9. A guide catheter is placed into the desired common carotid
artery. If a guiding catheter is placed, it can be used to deliver
contrast media directly to further assess carotid anatomy.
10. A 10f-12f(3.3-4.0 mm) (approximate) cooling catheter is
subsequently filled with saline and all air bubbles are
removed.
11. The cooling catheter is placed into the carotid artery via the
guiding catheter or over the guidewire. Placement is confirmed with
flouroscopy.
12. Alternatively, the cooling catheter tip is shaped (angled or
curved approximately 45 degrees), and the cooling catheter shaft
has sufficient pushability and torqueability to be placed in the
carotid without the aid of a guide wire or guide catheter.
13. The cooling catheter is connected to a pump circuit also filled
with saline and free from air bubbles. The pump circuit has a heat
exchange section that is immersed into a water bath and tubing that
is connected to a peristaltic pump. The water bath is chilled to
approximately 0.degree. C.
14. Cooling is initiated by starting the pump mechanism. The saline
within the cooling catheter is circulated at 5 cc/sec. The saline
travels through the heat exchanger in the chilled water bath and is
cooled to approximately 1.degree. C.
15. It subsequently enters the cooling catheter where it is
delivered to the heat transfer element. The saline is warmed to
approximately 5-7.degree. C. as it travels along the inner lumen of
the catheter shaft to the end of the heat transfer element.
16. The saline then flows back through the heat transfer element in
contact with the inner metallic surface. The saline is further
warmed in the heat transfer element to 12-15.degree. C., and in the
process, heat is absorbed from the blood, cooling the blood to
30.degree. C. to 32.degree. C.
17. The chilled blood then goes on to chill the brain. It is
estimated that 15-30 minutes will be required to cool the brain to
30 to 32.degree. C.
18. The warmed saline travels back down the outer lumen of the
catheter shaft and back to the chilled water bath where it is
cooled to 1.degree. C.
19. The pressure drops along the length of the circuit are
estimated to be 2-3 atmospheres.
20. The cooling can be adjusted by increasing or decreasing the
flow rate of the saline. Monitoring of the temperature drop of the
saline along the heat transfer element will allow the flow to be
adjusted to maintain the desired cooling effect.
21. The catheter is left in place to provide cooling for 12 to 24
hours.
22. If desired, warm saline can be circulated to promote warming of
the brain at the end of the procedure.
The invention has also been described with respect to certain
embodiments. It will be clear to one of skill in the art that
variations of the embodiments may be employed in the method of the
invention. For example, the tube sections may employ materials
other than metals or rubbers, so long as the materials have
characteristics similar to those described above. Accordingly, the
invention is limited only by the scope of the appended claims.
* * * * *